1. Field of the Present Invention
The present invention relates to a lithographic apparatus and a method for manufacturing a device.
2. Related Art
Lithography is widely recognized as a key process in manufacturing integrated circuits (ICs) as well as other devices and/or structures. A lithographic apparatus is a machine, used during lithography, which applies a desired pattern onto a substrate, such as onto a target portion of the substrate. During manufacture of ICs with a lithographic apparatus, a patterning device (which is alternatively referred to as a mask or a reticle) generates a circuit pattern to be formed on an individual layer in an IC. This pattern may be transferred onto the target portion (e.g., comprising part of, one, or several dies) on the substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (e.g., resist) provided on the substrate. In general, a single substrate contains a network of adjacent target portions that are successively patterned. Manufacturing different layers of the IC often requires imaging different patterns on different layers with different reticles. Therefore, reticles must be changed during the lithographic process.
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
A projection system is provided for carrying out the final stage of the imaging of the pattern onto the layer of radiation-sensitive material by projecting a patterned radiation beam from the patterning device to the substrate. The projection system comprises various elements, referred to below as “radiation-adjusting elements”, which are capable of interacting with a radiation beam in order to alter the properties thereof. The overall configuration of these elements defines how the projection system operates.
One or more of the radiation-adjusting elements may be provided with an actuator for adjusting the state of the element, for example its position, shape and/or orientation. The projection system elements may be reflective (e.g., a mirror) or transmissive (e.g., a lens), for example.
A sensor may be provided for measuring the state of a given radiation-adjusting element. The sensor may measure the position, shape and/or orientation of the radiation-adjusting element, for example. The actuator for the radiation-adjusting element may be configured to operate by reference to the output from the sensor, for example by means of a control loop.
Means may be provided for mechanically isolating certain radiation-adjusting elements from certain other elements of the lithography apparatus. The mechanical isolation may inhibit (reduce) propagation of vibrations, for example. The mechanical isolation may isolate an actuator for a given radiation-adjusting element from a corresponding sensor for measuring the state of that element, for example.
Despite the presence of these mechanical isolation means, some vibrations may still propagate between elements of the projection system that are nominally “isolated” by these means, thus leading to a reduction in performance of the projection system. In the case where vibrations propagate between an actuator for a given radiation-adjusting element and a corresponding sensor for measuring the state of that element, for example, the performance of the sensor (affecting overlay accuracy for example) and/or the performance of control systems that use the sensor output (affecting throughput because of reduced stability and/or longer setpoint convergence times for example) may be reduced.